How do I allow Key Characters?

[eluser]Isos[/eluser]
Hi,
how can I allow Key Characters in form post requests?
I am trying to send a the source code of the user's browser using [removed] document.documentElement[removed]; .. So, after submitting I get this notice: Disallowed Key Characters. .. how can I allow that only for a certain form post request?

Thanks

[eluser]Mirage[/eluser]
What's the URL you're posting to look like?